1. Field of the Invention
The present invention relates to a test device for locating faults in a two-wire line. The test device is based on detecting in-line current and consequently enables a short circuit, an insulation fault or a low resistance shunt to determine at a remote location. Generally speaking, the invention deals with sensing the current along an electrical two-wire line at a predetermined location to locate a resistive loop in the line or to control switching of the line at that location with another two-wire line or to select one of two loads terminating the line.
Reference is made hereinafter to the particular case in which the two-wire line is a telephone subscriber loop serving a telephone subscriber terminal from a switching facility at the associated telephone exchange.
2. Description of the Prior Art
The prior test devices for locating faults in a telephone subscriber line are costly and work in a rudimentary fashion. The test device disconnects the remainder of the line at the telephone terminal end and loops the line at the location in question to perform remote continuity and/or insulation testing measurements using a testing and measuring apparatus available in the associated switching facility. The measurements confirm whether the detected fault is located in a line on the switching facility side or telephone terminal side and aid in deciding whether (1) a maintenance team equipped with heavy-duty gear should be sent to repair the line or (2) a subscriber should call in a specialist to repair his telephone terminal. After a given period of time, the test device returns to its original position.
A recent development in telephone subscriber installations or analogous telephone terminals, as well as in testing and measuring apparatus, enables the current flowing through the line at a predetermined location to be more accurately measured. This location may coincide with an input of a telephone terminal or a line-to-exchange frame junction. Furthermore, this development permits remote controlled switching, where necessary, from the telephone exchange. This application is especially advantageous when substituting a spare two-wire line for a faulty working line.